1. Field of the Invention
The present invention relates to a method, an apparatus, a program, and a recording medium for image processing of converting colors to allow a color-weak person to distinguish colors more easily without making a document creator or a person with common color vision feel a sense of incongruity.
2. Description of the Related Art
In recent years, advancement of color image output technology for displaying and printing out color images has allowed individuals and companies to use various colored characters and color images to create documents and web pages. In such documents, the colors themselves are often made to carry important information by using colored characters and the like for notations to draw attention and for grouping graphs. To understand the contents of such documents correctly, the characters and images need to be recognized and further, the differences between the colors used in the documents need to be distinguished.
Even for such documents using various colors, color information is difficult to be distinguished for people with color vision impairment. For example, for a color vision with difficulty in distinguishing between red and green, of a graph using red, green, and blue, the red and the green are difficult to be identified or are completely impossible to be identified, and thus the graph may be just recognized as a graph consisting of two elements, “blue” and “other than blue”. Furthermore, because color image output apparatuses are able to express multiple colors, coloring that is difficult to recognize even for people with common color vision may sometimes obtained.
FIG. 1 is an example of a document including colored characters, a pie chart, and a photograph. In the coloring of the pie chart illustrated in FIG. 1, differences between colors are relatively recognizable because the pie chart has a comparatively large area and the colors are adjacent to each other. To read the pie chart, the pie chart needs to be related to a legend, but the legend portion has a small area and thus the difference between their colors are difficult to be recognized and the association between the pie chart and the legend is difficult. Similarly, as to colored characters, if the font of the characters is fine like the Mincho type and the size of the characters is small, the colored characters used are hard to be recognized. As to images of natural objects such as photographs, the objects are often empirically relatable to color names (e.g. leaves are green and human faces are in skin colors), and the coloring itself often has no meaning.
According to physiological and medical studies on human color visions, certain types of color vision impairment are known, like red-green color blindness with difficulty in distinguishing red and green as exemplified above, yellow-blue color blindness, and total color blindness. Recently, Color Universal Design Organization (CUDO, a non-profit organization) suggests calling various color visions, not by grouping color visions based on whether each color vision is normal or abnormal, but by their type names such as common (C) type, protanope (P) type (severe or mild) corresponding to red-green color blindness or color weakness, deuteranope (D) type (severe or mild) corresponding to red-green color blindness or color weakness, tritanope (T) type corresponding to yellow-blue color blindness, and achromatic (A) type corresponding to total color blindness. Further, CUDO suggests calling people having the C type color vision “people with common color vision” and the others having a weakness in recognizing colors as “color-weak people”.
To make colors easily recognizable in consideration of such color vision impairment, techniques have been proposed in which the colors used in a document are extracted and, if the extracted colors includes a combination of colors that is hard to distinguish from each other, (1) the colors are adjusted (for example, see Japanese Patent Application Laid-open No. 2007-293832), (2) the filled areas in graphs and the like are hatched (for example, see Japanese Patent Application Laid-open No. 2008-77307), and (3) the filled areas are fringed (for example, see Japanese Patent Application Laid-open No. 2001-293926).
Furthermore, as a display that is easily recognized both by people with color vision impairment and by people with common color vision, a display object that is seen in red and green when viewed from the front but seen in green and blue respectively when viewed obliquely is also available (see Japanese Patent Application Laid-open No. 2007-271946).
However, in the above method (1), because the area of the legend in the graph is small, the difference between the colors is difficult to be recognized, and thus the colors need to be changed largely (for example, when there is little difference between their lightnesses, even changing the b* component in CIELAB color space by Δb*=45 may not make the colors distinguishable), and a person who knows the original coloring such as the creator of that document may feel a sense of incongruity.
In the method (2), because cyclically inserting diagonal lines in the filled areas of the graph changes the form of the image, similarly to the method (1), the creator of the original image may feel a sense of incongruity, and color-weak people may need to recognize the form of the hatching and then identify the association between the graph and the legend, and thus the graph is less intuitively readable than the color differences. Furthermore, when the area of the legend is too small and the hatching pattern is coarse, a cycle of that pattern may not fit into the legend and thus the hatching is not sufficiently effective.
In the method (3), although isolation of areas is recognizable by the fringes around the filled areas, unless the difference between the colors is not recognizable, the association between the graph and the legend is not possible, and thus this method is not a fundamental solution.
In Japanese Patent Application Laid-open No. 2007-271946, the state of the surface of each area of the display object is made different by the difference between hues of the areas. However, because the colors are changed, people with common color vision feel a sense of incongruity and because of the structure of the display object, application to printouts output from an image forming apparatus is difficult.